The purpose of this protocol is to determine whether magnetic resonance angiography (MRA) and captopril magnetic resonance renography (MRI) can provide comprehensive evaluation of patients at risk for renovascular hypertension. Although renovascular hypertension (renal artery stenosis causing high blood pressure) is unusual, it nonetheless represents a correctable form of hypertension. The current methods of evaluating patients for renovascular hypertension are cumbersome and include Doppler sonography, captopril renography, MRA and angiography. The purpose of this protocol is to test the current gold standards, captopril renography and angiography against a combination of MRA and captopril MR renography. For this study, the at-risk patient undergoes a conventional captopril nuclear medicine renogram followed by an MR renogram and MRA. The patient also breathes an oxygen-rich-gas known as carbogen which is used to test for renal ischemia. To date, we have accrued 6 volunteers and 16 patients to this protocol. We anticipate continued patient accrual to this protocol over the coming year.